Pressure sensitive copying sheet



v V 3,167,443 PRESSURE SENSITIVE COPYING SHEET John F. McHugh, Brooklyn, N.Y., and Donald J.

Lazzarini, North Bergen, N.J., assignors to Interchemical Corporation, a corporation of Ohio No Drawing. Filed July 7, 1961, Ser. No. 122,393 2 Claims. (Cl. 117-365) This invention relates to pressure-sensitive relatively heat-insensitive, non-carbon copy sheet material having a blushed lacquer film coated on one of its surfaces.

United States Patent 2,306,525, issued December 29, 1942, disclosed a multi-tone coated material comprising a base coated with a film that had been allowed to blush, a method and a type of material now well known in the art. Blushed films are more or less opaque but application of sufficient heat or pressure renders a properly made blushed film much more transparent. The general method of making such materials is the evaporation of the solvent from a film-forming resin solution comprising a resin dissolved in a liquid that is a good solvent for the resin and also containing a comparatively poor solvent for the resin, the relative vapor pressures being such that the concentration of the poor solvent greatly increases as evaporation proceeds and the film becomes more or less opaque. Evaporation of the good solvent is preferably at least six times more rapid than that of the poor solvent. The application of pressure, heat, or both to the dried filmwill produce relatively transparent areas. The practical utilization of this principle entails the consideration of many properties, desirable and undesirable, and many compromises between interrelated ones.

Such a coating composition is described for example in United States Patent 2,665,262, issued January 5, 1954, where the essential solid ingredients are a particular type of vinyl copolymer and a finely-divided inert solid material of low tinting strength.

There is a considerable demand for the development of good substitutes for carbon paper and similar ink transfer materials. A sheet sufficiently pressure sensitive to display high visual contrast in color or brightness between the areas subjected to pressure and those relatively unpressed would answer the purpose. The prospective designer of such a sheet is confronted with many problems other than attainment of the desired contrast and pressure sensitivity. The sheets should function properly in manifolds of many copies. permanent as possible and therefore should have comparatively low sensitivity to temperature changes and reasonable immunity to other hazards.

It has noW been found that non-carbon copy papers of improved pressure sensitivity and reduced heat sensitivity may be made by coating suitable paper with certain blushed lacquer films. The pressure sensitivity is enhanced so that typed or hand-written copies may be made without the need for typing ribbons or carbon papers. The papers are also useful for providing copies of embossed printed matter from pressure-operated recording devices. The coating compositions may be applied by conventional methods on colored paper or on color-coated white paper.

The pressure-sensitive copying sheets of this invention may also be used to make designs and drawings either by tracing over already printed or drawn figures or by making original drawings or effects on the paper directly. As an example of the latter, complex scroll work may be formed by movements of a brush in contact with the surface of the paper.

Aging tests were made by imaging the prepared sheets via an electric typewriter and then making reflectance curves of the imaged areas and the backgrounds. The

The copies should be as nited States Patent O printed sheets were allowed to stand for some months, additional reflectance measurements being made at intervals. Comparison of the reflectance of the background with that of the imaged area is a measure of the pressure sensitivity. The ratio of similar reflectance measurements taken later, and compared with the original ratio is a measure of the aging qualities of the copy. Another factor of importance is curling of the paper; preferably there should be no curl but a slight curl is tolerated. It goes without saying that the blushed film should have adequate adhesion to the backing.

Temperature sensitivity of the coatings was evaluated by placing the coating against a heated bar having a temperature gradient, the exposure times and pressures being constant. The temperatures rendering the coating adequately transparent were recorded. The pressuresensitive coatings of this invention become suitably transparent or translucent only at temperatures well in excess of C., the boiling point of water, and thus are not injured by heat when stored near the usual types of hot water or steam heating units.

In the examples that follow parts are parts by weight.

Example 1 7.8 parts of Witco aluminum stearate #36 were dispersed in a solution of 7.8 parts cellulose acetate E3983 in 59.3 parts acetone, 20.4 parts Amsco Hi-Flash Naphtha (a liquid hydrocarbon mixture having a boiling range of 154-185 C., a kauri-butanol value of 87.5, and Weighing 7.24 lbs. per gallon), 3.1 parts of diethyl phthalate, and 1.6 parts of tricresyl phosphate. A copying paper made with this composition applied on a standard weight carbonizing tissue showed very good blush and was insensitive to temperatures below 116 C. Printed copies were readily made in a 15-sheet manifold using a standard electric typewriter and copies so made showed no reduction in contrast between the background and the printing after several months of storage. The flow properties of the composition were such that speedy industrial coating methods and apparatus were applicable.

Example 2 5 parts of cellulose acetate E-398-3 were dissolved in 38 parts acetone. 13 parts of Amsco Hi-Flash Nap'htha, 3 parts of tricresyl phosphate and 5 parts of a lowagel strength aluminum stearate were added. This composition when made up into copying paper had good pressure sensitivity, comparatively low temperature sensitivity and printed copies had good aging qualities. The overall quality, however, was not quite up to that recited in Example 1. The pressure sensitivity was inferior to that in Example 1, but measurement of the temperature sensitivity gave a figure of C.

Example 3 7.5 parts of cellulose acetate E-398-3 were dissolved in 37.5 parts acetone. 7.5 parts of magnesium stearate in 16.6 parts xylol, 19.7 parts acetone, 6.2 parts diethyl phthalate, 1.4 parts tricresyl phosphate, and 3.6 parts n-butyl stearate were stirred in. Copying paper made with this composition had excellent pressure sensitivity and comparatively low temperature sensitivity. The aging qualities were good.

Example 1 was repeated but using aluminum stearates of progressively higher gel strength up to Witco aluminum stearate #50. Satisfactory copy papers were made in all cases, but they were somewhat inferior to Example 1 copy papers. Other compositions were made varying the amount and type of plasticizers, solvents, resins, and stearates. It was also found that Carbowax 20-M was a fairly good substitute for aluminum stearate, as

were also'carnauba Wax and Acrawax C'. Other stearates that were fairly good, in decreasing order of effectivness, were sodium stearate, magnesium stearate, and calcium stearate. The combination of diethyl phthalate (primarily for pressure sensitivity) with tricresyl phosphate or n-butyl stearate (for heat resistance) gave the best overall results, although either alone was effective and closely related substances were fairly good but clearly inferior to the preferred combination. For example dibutyl phthalate was definitely less elfective than diethyl phthalate. Dimethyl and diisopropyl phthalates were close to diethyl phthalate in the results. The boiling range of the naphtha selected should not vary too much from ISO-190 C. nor the kauri-butanol value too far from 8590, but other poor solvents may be used as shown in Example 3. Although acetone is preferred for the favorable flow properties it imparts to the composition, other suitable volatile solvents may be used, methyl ethyl ketone for example. The relative amount of the two solvents is of more importance. The naphtha may be varied from 11 to 14 parts and acetone from 34 to 38 parts for 5 parts of the cellulose acetate Without changing the blushing properties of the composition. Tric-resyl phosphate or n-butyl stearate may be varied from to 13- parts and diethyl phthalate from 0 to parts, but a substantial amount of plasticizer must be present. Each plasticizer may be used alone, although preferably the plasticizers are used in combinations. The ability tov blush decreases with increasing proportions of the alkyl phthalate and with decreasing proportions of the poor solvent. When the blushing qualities are impaired by the addition of comparatively large quantities of phthalate plasticizers, opacity may be improved by the addition of metal stearates, carnauba Wax, or other Waxy substances mentioned above. The amount of metal stearates may be varied to suit each combination. The preferred cellulose acetate E-398-3, has an acetyl content of about 40%, a melting point of 230 C. to 250 C., and a viscosity of 6.814.8 poises as determined by A.S.T.M. method D1343-56 in the solution described as Formula A in the A.S.T.M. method D871-56. Similar products made with methyl methacrylate (Lucite), or vinyl acetatevinyl' chloride copolymers, or /2-sec. nitrocellulose did not match the overall de-' having a softening point of -55 C. Acrawax C is a stearamide having a softening point of l40143 C.

What is claimed is:

1. A pressure-sensitive copying sheet comprising a non-metallic supporting base and having coated thereon a visibly opaque, pressure-sensitive blushed film of contrasting color, the film comprising (a) cellulose acetate having a softening point of 230 to 250 C. and an acetyl content of about 40% and a viscosity of 6.814.8 poises'as determined by A.S.T.M.method D-1343-56 in the solu-, tion described as Formula A in the A.S.T.M. method D- 871-56 and (a) a plasticizer selected from the group consisting of nbutyl stearate, tricresyl phosphate, and alkyl phthalates, the alkyl group having 1-4 carbon atoms, the Weight of plasticizer present being equal to form about onehalf to about two and one-half times the weight, of the cellulose acetate, said blushed coating being insensitive to temperatures below C. I i

2. A pressure-sensitive copying sheet as described in claim 1, wherein the blushed film also contains a substantial amount of a waxy substance selected from the group consisting of aluminum stearate, sodium stearate, calcium stearate, magnesium stearate, carnauba wax, polyethylene glycol having a softening point of 50-55 C., and "a steararnide having a softening point of 143 C.

References Cited in the file of this patent. I

UNITED STATES PATENTS 

1. A PRESSURE-SENSITIVE COPYING SHEET COMPRISING A NON-METALLIC SUPPORTING BASE AND HAVING COATED THEREON A VISIBLY OPAQUE, PRESSURE-SENSITIVE BLUSHED FILM OF CONTRASTING COLOR, THE FILM COMPRISING (A) CELLULOSE ACETATE HAVING A SOFTENING POINT OF 230* TO 250*C. AND AN ACETYL CONTENT OF ABOUT 40% AND A VISCOSITY OF 6.8-14.8 POISES AS DETERMINED BY A.S.T.M. METHOD D-1343-56 IN THE SOLUTION DESCRIBED AS FORMULA A IN THE A.S.T.M. METHOD D871-56 AND (A) A PLASTICIZER SELECTED FROM THE GROUP CONSISTING OF N-BUTYL STEARATE, TRICRESYL PHOSPHATE, AND ALKYL PHTHALATES, THE ALKYL GROUP HAVING 1-4 CARBON ATOMS, THE WEIGHT OF PLASTICIZER PRESENT BEING EQUAL TO FORM ABOUT ONEHALF TO ABOUT TWO AND ONE-HALF TIMES THE WEIGHT OF THE CELLULOSE ACETATE, SAID BLUSHED COATING BEING INSENSITIVE TO TEMPERATURES BELOW 100*C. 